[PATCH 1/3] serial: qcom-geni: fix hard lockup on buffer flush

[Johan Hovold]

The Qualcomm GENI serial driver does not handle buffer flushing and used
to print garbage characters when the circular buffer was cleared. Since
commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo") this
instead results in a lockup due to qcom_geni_serial_send_chunk_fifo()
spinning indefinitely in the interrupt handler.

This is easily triggered by interrupting a command such as dmesg in a
serial console but can also happen when stopping a serial getty on
reboot.

Fix the immediate issue by printing NUL characters until the current TX
command has been completed.

Fixes: 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo")
Reported-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Signed-off-by: Johan Hovold <johan+linaro@xxxxxxxxxx>
---
 drivers/tty/serial/qcom_geni_serial.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 2bd25afe0d92..1d5d6045879a 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -862,7 +862,7 @@ static void qcom_geni_serial_send_chunk_fifo(struct uart_port *uport,
 		memset(buf, 0, sizeof(buf));
 		tx_bytes = min(remaining, BYTES_PER_FIFO_WORD);
 
-		tx_bytes = uart_fifo_out(uport, buf, tx_bytes);
+		uart_fifo_out(uport, buf, tx_bytes);
 
 		iowrite32_rep(uport->membase + SE_GENI_TX_FIFOn, buf, 1);
 
-- 
2.44.1